Ultrathin-Gap MXene/Carbon Nanotube Microsupercapacitors for High-Performance Alternating Current-Line Filtering

The continued miniaturization of modern electronic devices has created an urgent demand for next-generation AC-line filtering capacitors capable of replacing conventional aluminum electrolytic capacitors. Here, we report a high-performance AC-line filter based on MXene/CNT liquid crystal, fabricated into cross-finger electrodes via spin coating followed by supercritical drying. Precise control over the interelectrode gap width was achieved using femtosecond laser direct writing, enabling gap sizes as small as 5 µm. Systematic electrochemical characterization reveals that the electrode with a 5 µm gap width exhibits an ultralow equivalent series resistance of 0.15 Ω cm2 and a highly negative phase angle of –84° at 120 Hz. Owing to rapid ion transport within MXene/CNT architecture and the ultranarrow electrode spacing, the device delivers superior high-frequency response with a 0.1 ms relaxation time constant, and efficient AC-line filtering performance. These results demonstrate the strong potential of MXene-based microsupercapacitors as compact, high-performance alternatives to traditional electrolytic capacitors for powering next-generation electronic systems.